THE INFLUENCE OF WATER ACTIVITY ON 3 GENOTYPES OF SNAP BEAN (PHASEOLUS-VULGARIS L) IN RELATION TO MECHANICAL DAMAGE RESISTANCE

Mechanical damage has been identified as an important cause of vigour loss and decreased seed quality and resistance to this damage in snap bean (Phaseolus vulgaris L.) has been associated with seed coat colour and moisture content. Two near-isogenic lines (white and dark-seeded) selected for mechanical damage resistance (MDR) and a commercial cult ivar (white seeded) of snap bean were studied by dropping seeds in a f ree fall impact test from a height of 2.0 m. Resistance to compression was also tested using a texture analyzer, TA.XT2. The dark seeded iso genic line had a higher germination after impact than the white seeded isogenic line followed by the commercial cultivar at each water activ ity (a(w)) tested from 0.35 to 0.65 in 0.1 increments, Greater MDR to impacts in the dark seeded line was attributed to higher lignin conten t in the seed coats and better cotyledon to cotyledon attachment. The germination results after compression showed that genotype differences were observed only at 0.65 a(w), whereby the commercial cultivar rema ined the most susceptible and the white-seeded isogenic line the least susceptible. In conclusion, seed moisture content was the major gover ning factor responsible for the degree of susceptibility to mechanical damage while at each a(w) tested genotypic differences to impact dama ge were measured.